With a fretted and stringed electric or electronic musical instrument, musical sound is produced with various tones generated through detection of the timings at which strings are picked and the locations of the fret members against which the strings being picked are pressed on the fingerboard. The timing at which a string is picked can be detected by the use of an electromagnetic pickup device responsive to relatively low frequency vibrations of the string. On the other hand, the location of the fret member with which a string is pressed into contact is detected by a fret-position detector using piezoelectric transducer elements respectively engaging the strings of the musical instrument. Each of the piezoelectric transducer elements is electrically activated to produce supersonic vibrations in the associated string and the supersonic vibrations thus produced in the string are transmitted to the fret member with which the string is currently pressed into contact. The vibrations which have reached the particular fret member are then reflected from the fret member and are transmitted backwardly to the piezoelectric transducer element. The supersonic vibrations returned to the piezoelectric transducer element mechanically activate the transducer element to produce an electric output signal when the vibrations are received by the transducer element. The signal thus produced by the piezoelectric transducer element is monitored to determine the time interval intervening between the generation of the supersonic vibrations in the sound and the generation of the signal by the supersonic vibrations returned to the transducer element. An electronic musical instrument of this type is disclosed in U.S. Pat. No. 4,723,468.
The fret-position detector used in a prior-art electronic musical instrument of the described type depends for its operation on the period of time for which supersonic vibrations are transmitted to and from a fret member. For this reason, it is of critical importance for the reliability of operation of the instrument that the supersonic vibrations echoed from the fret member be strictly discriminated from various spurious vibrations which may be transmitted to the piezoelectric transducer element to act as noises to the echoed signal vibrations. The spurious vibrations which may be transmitted to the piezoelectric transducer element include vibrations echoed from a bridge member carrying the piezoelectric transducer elements of the fret-position detector per se. Such spurious vibrations are produced in the bridge member in direct response to the supersonic vibrations generated in the transducer elements and are reflected from the bridge member directly to each of the transducer elements.
To eliminate the effects of such noise vibrations which may be transmitted to the piezoelectric transducer elements of the fret-position detector, the electric output signal produced by each of the transducer elements is analyzed to detect the cyclically occurring peaks of the signal waveform and determine the time interval intervening between successive two of the peaks detected. A problem still arises in this manner of detecting the fret positions because, primarily, the peaks of the signal waveform produced by the fret-position detector are subject to irregular variation depending on the conditions in which the string through which the supersonic vibrations are transmitted is held in contact with the fret member to which the vibrations are transmitted. Such irregular variation in the peaks of the signal waveform may cause an error in the time interval determined on the basis of the signal from the fret-position detector. When such an error is grown to a critical degree after the instrument is used for an extended period of time, deviation may be caused between the note of the sound intended to be produced by the player of the instrument and the note of the sound actually produced by the instrument in response to the signal from the fret-position detector.
The present invention first contemplates elimination of these drawbacks of a prior-art electronic musical instrument using a known fret-position detector. It is, accordingly, an important object of the present invention to provide an electronic musical instrument in which the location of the fret member with which a string being picked is pressed into contact can be accurately determined without respect to the spurious vibrations which may be transmitted to the piezoelectric transducer elements of the fret-position detector included in the instrument.
There is another important problem which results from the fact that the fret-position detector depends for its operation on the time interval for which supersonic vibrations are transmitted to and from a fret member. Such a time interval is however subject to fluctuations due to deformation of the neck portion of the instrument as caused by the tensions maintained in the strings and to lateral displacement of the strings on the fret members. In case such fluctuations in the time interval are of a critical degree, deviation may also be caused between the note of the sound intended to be produced by the player of the instrument and the note of the sound actually produced by the instrument in response to the signal from the fret-position detector.
Thus, the present invention further contemplates elimination of such a drawback of a prior-art electronic musical instrument using a known fret-position detector. Accordingly, it is another important object of the present invention to provide an electronic musical instrument capable of accurately determining the location of a fret member without respect to the fluctuations which may be caused in the time interval determined by the fret-position detector included in the instrument.
In the meantime, there is known and used a "bent-string" playing technique with which a string is forced to sidewise slide on a fret member to produce a rising intonation. When such a technique is used during playing of a musical instrument having a fret-position sensor of the described nature, the sensor could not detect the mode of playing and for this reason the sound producing system could not produce the player's intended rising intonation. This is primarily because of the fact that the sensor depends for its operation merely on the period of time for which vibrations are transmitted to a fret member and backwardly from the fret member to the sensor. To eliminate such an inconvenience, an electronic musical instrument has been proposed which uses probe elements respectively held in engagement with the individual strings of the instrument. Each of the probe elements is located to intercept the path of light in a photocoupling unit which thus produces an electric signal variable with the lateral displacement of the string engaged by the associated probe element. An electronic musical instrument of this type is disclosed in Japanese patent application No. 62-083289.
The features of these two types of prior-art musical instruments could be combined to provide an electronic musical instrument allowing the player of the instrument to use the bent-string playing technique. In such an electronic musical instrument having the combined features of the two types of prior-art instruments, the signal produced from the photocoupling unit is produced upon comparison with a signal produced when the associated string remains in a non-bent state extending straight on a fret member. It is thus of critical importance that the value of the signal produced responsive to a string in such a non-bent state be accurately determined by the photocoupling unit. Difficulties are however encountered in accurately determining such a value because, primarily, of the fact that the lateral position of each string on a fret member is subject to variation depending on the tension in the string.
The present invention further contemplates elimination of such a drawback of an electronic musical instrument having the combined features of the two types of prior-art instruments. It is, accordingly, still another important object of the present invention to provide an improved electronic musical instrument having a bent-string sensor and capable of accurately determining a non-bent state of a string.